U.S. patent application number 11/096009 was filed with the patent office on 2006-10-05 for pulse oximetry sensor and technique for using the same on a distal region of a patient's digit.
Invention is credited to Paul D. Mannheimer.
Application Number | 20060224058 11/096009 |
Document ID | / |
Family ID | 36603591 |
Filed Date | 2006-10-05 |
United States Patent
Application |
20060224058 |
Kind Code |
A1 |
Mannheimer; Paul D. |
October 5, 2006 |
Pulse oximetry sensor and technique for using the same on a distal
region of a patient's digit
Abstract
A sensor may be placed on a distal portion of a patient's finger
or toe to obtain pulse oximetry measurements. The distal portion of
a digit contains few if any large vascular structures that could
adversely affect pulse oximetry measurements, but the distal
portion does contain microvasculature that carries arterial blood
that facilitates pulse oximetry measurements. The sensor may
include an emitter and a detector that are spaced apart by an
appropriate distance so that they may be located on the distal
portion of a patient's digit during pulse oximetry
measurements.
Inventors: |
Mannheimer; Paul D.;
(Danville, CA) |
Correspondence
Address: |
FLETCHER YODER (TYCO INTERNATIONAL, LTD.)
P.O. BOX 692289
HOUSTON
TX
77269-2289
US
|
Family ID: |
36603591 |
Appl. No.: |
11/096009 |
Filed: |
March 31, 2005 |
Current U.S.
Class: |
600/323 ;
600/344 |
Current CPC
Class: |
A61B 5/14552 20130101;
A61B 5/6826 20130101; A61B 5/6838 20130101 |
Class at
Publication: |
600/323 ;
600/344 |
International
Class: |
A61B 5/00 20060101
A61B005/00 |
Claims
1. A pulse oximetery sensor adapted for use on a patient's digit,
wherein the patient's digit includes a distal portion having a
distal bone covered with skin and tissue and wherein the distal
portion has a length L as measured from a tip of the distal portion
to a transverse fold of skin located generally at a joint between
the distal bone and an adjacent bone, the pulse oximetery sensor
comprising: an emitter and a detector adapted to be located on a
distal region of the distal portion of the patient's digit, wherein
the distal region is measured as extending from the tip of the
distal portion to a location spaced no more than approximately 30%
of the length L from the tip.
2. The pulse oximetry sensor, as set forth in claim 1, comprising:
a substrate on which the emitter and detector are disposed; and a
wrap on which the substrate is disposed, the wrap being configured
to secure the emitter and detector to the distal region of the
distal portion of the patient's digit.
3. The pulse oximetry sensor, as set forth in claim 1, wherein the
emitter and the detector are adapted to operate in a transmission
mode.
4. The pulse oximetery sensor, as set forth in claim 1, wherein the
emitter and the detector are wholly disposed in the distal
region.
5. The pulse oximetry sensor, as set forth in claim 1, wherein the
emitter and the detector have center points that are located in the
distal region.
6. The pulse oximetry sensor, as set forth in claim 5, wherein a
portion of at least one of the emitter and the detector is located
on the distal portion outside the distal region.
7. The pulse oximetry sensor, as set forth in claim 1, wherein the
patient's digit comprises a finger, and wherein the distal bone
comprises a distal phalange.
8. The pulse oximetry sensor, as set forth in claim 1, wherein the
distal region is measured as extending from the tip of the distal
portion to a location spaced no more than approximately 20% of the
length L from the tip.
9. The pulse oximetry sensor, as set forth in claim 1, comprising:
a clip-style sensor in which the emitter and detector are
disposed.
10. A method for performing pulse oximetery, the method comprising:
placing an emitter and a detector of a pulse oximetery sensor on a
distal region of a distal portion of a patent's digit, wherein
distal portion of the patient's digit includes a distal bone
covered with skin and tissue and wherein the distal portion has a
length L as measured from a tip of the distal portion to a
transverse fold of skin located generally at a joint between the
distal bone and an adjacent bone, and wherein the distal region of
the distal portion of the patient's digit is measured as extending
from the tip of the distal portion to a location spaced no more
than approximately 30% of the length L from the tip.
11. The method, as set forth in claim 10, wherein placing
comprises: wrapping an adhesive bandage about the patient's digit
to hold the emitter and the detector of the pulse oximetry sensor
in place on the distal region.
12. The method, as set forth in claim 10, wherein placing
comprises: clipping a sensor to the patient's digit to hold the
emitter and the detector of the pulse oximetry sensor in place on
the distal region.
13. The method, as set forth in claim 10, comprising: positioning
the emitter on a top portion of the distal region of the distal
portion of the patient's digit; positioning the detector on a
bottom portion of the distal region of the distal portion of the
patient's digit; and operating the emitter and the detector in a
transmission mode.
14. The method, as set forth in claim 10, comprising: positioning
the emitter and the detector on a top portion of the distal region
of the distal portion of the patient's digit; and operating the
emitter and the detector in a reflectance mode.
15. The method, as set forth in claim 10, comprising: positioning
the emitter and the detector on a bottom portion of the distal
region of the distal portion of the patient's digit; and operating
the emitter and the detector in a reflectance mode.
16. The method, as set forth in claim 10, comprising: positioning
the emitter and the detector side by side in the distal region of
the distal portion of the patient's digit; and operating the
emitter and the detector in a transmission mode.
17. The method, as set forth in claim 10, wherein the distal region
of the distal portion of the patient's digit is measured as
extending from the tip of the distal portion to a location spaced
no more than approximately 20% of the length L from the tip.
18. A method of manufacturing a pulse oximetry sensor to monitor a
distal region of a distal portion of a patient's digit, wherein the
distal portion includes a distal bone covered with skin and tissue
and wherein the distal portion has a length L as measured from a
tip of the distal portion to a transverse fold of skin located
generally at a joint between the distal bone and an adjacent bone,
and wherein the distal region is measured as extending from the tip
of the distal portion to a location spaced no more than
approximately 30% of the length L from the tip, the method
comprising: fabricating a pulse oximetry sensor to include an
emitter and a detector adapted to be located on the distal region
of the distal portion of the patient's digit.
18. The method, as set forth in claim 18, wherein fabricating
comprises: disposing the emitter and the detector on a structure
that comprises a flat substrate.
19. The method, as set forth in claim 18, wherein fabricating
comprises: disposing the flat substrate on a flexible wrap.
20. The method, as set forth in claim 19, wherein the flexible wrap
is adhesively coated.
21. The method, as set forth in claim 18, wherein fabricating
comprises: disposing the emitter on one side of a clip and
disposing the detector on another side of a clip.
22. The method, as set forth in claim 18, wherein the distal region
of the distal portion of the patient's digit is measured as
extending from the tip of the distal portion to a location spaced
no more than approximately 20% of the length L from the tip.
23. A pulse oximetry system comprising: a pulse oximetry monitor;
and a pulse oximetery sensor having an emitter and a detector
adapted to be located on a distal region of a distal portion of a
patient's digit, wherein the distal portion of the patient's digit
includes a distal bone covered with skin and tissue and wherein the
distal portion has a length L as measured from a tip of the distal
portion to a transverse fold of skin located generally at a joint
between the distal bone and an adjacent bone, and wherein the
distal region is measured as extending from the tip of the distal
portion to a location spaced no more than approximately 30% of the
length L from the tip.
24. The pulse oximetry system, as set forth in claim 23, wherein
the sensor comprises: a substrate on which the emitter and detector
are disposed; and a wrap on which the substrate is disposed, the
wrap being configured to secure the emitter and detector to the
distal region of the distal portion of the patient's digit.
25. The pulse oximetry system, as set forth in claim 23, wherein
the emitter and the detector are adapted to operate in a
transmission mode.
26. The pulse oximetery system, as set forth in claim 23, wherein
the emitter and the detector are wholly disposed in the distal
region.
27. The pulse oximetry system, as set forth in claim 23, wherein
the emitter and the detector have center points that are located in
the distal region.
28. The pulse oximetry system, as set forth in claim 27, wherein a
portion of at least one of the emitter and the detector is located
on the distal portion outside the distal region.
29. The pulse oximetry system, as set forth in claim 23, wherein
the patient's digit comprises a finger, and wherein the distal bone
comprises a distal phalange.
30. The pulse oximetry system, as set forth in claim 23, wherein
the distal region of the distal portion of the patient's digit is
measured as extending from the tip of the distal portion to a
location spaced no more than approximately 20% of the length L from
the tip.
31. A pulse oximetery sensor adapted for use on a patient's digit,
the pulse oximetery sensor comprising: an emitter adapted to
transmit light into the patient's digit; and a detector adapted to
receive the transmitted light from the patient's digit, the
detector being positioned to receive at least approximately 50% of
the received light from a distal region of a distal portion of the
patient's digit, wherein the distal portion of the patient's digit
includes a distal bone covered with skin and tissue and wherein the
distal portion has a length L as measured from a tip of the distal
portion to a transverse fold of skin located generally at a joint
between the distal bone and an adjacent bone, and wherein the
distal region is measured as extending from the tip of the distal
portion to a location spaced no more than approximately 30% of the
length L from the tip.
32. The pulse oximetry sensor, as set forth in claim 31,
comprising: a substrate on which the emitter and detector are
disposed; and a wrap on which the substrate is disposed, the wrap
being configured to secure the emitter and detector to the distal
region of the distal portion of the patient's digit.
33. The pulse oximetry sensor, as set forth in claim 31, wherein
the emitter and the detector are adapted to operate in a
transmission mode.
34. The pulse oximetery sensor, as set forth in claim 31, wherein
the emitter and the detector are adapted to be wholly disposed in
the distal region.
35. The pulse oximetry sensor, as set forth in claim 31, wherein
the emitter and the detector have center points that are adapted to
be located in the distal region.
36. The pulse oximetry sensor, as set forth in claim 35, wherein a
portion of at least one of the emitter and the detector is adapted
to be located on the distal portion outside the distal region.
37. The pulse oximetry sensor, as set forth in claim 35, wherein
the patient's digit comprises a finger, and wherein the distal bone
comprises a distal phalange.
38. The pulse oximetry sensor, as set forth in claim 31, wherein
the distal region of the distal portion of the patient's digit is
measured as extending from the tip of the distal portion to a
location spaced no more than approximately 20% of the length L from
the tip.
39. The pulse oximetry sensor, as set forth in claim 31, wherein
the detector adapted to receive the transmitted light from the
patient's digit, the detector being positioned to receive
approximately 50% to 80% of the received light from a distal region
of a distal portion of the patient's digit.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates generally to pulse oximetry
and, more particularly, to sensors used for pulse oximetry.
[0003] 2. Description of the Related Art
[0004] This section is intended to introduce the reader to various
aspects of art that may be related to various aspects of the
present invention, which are described and/or claimed below. This
discussion is believed to be helpful in providing the reader with
background information to facilitate a better understanding of the
various aspects of the present invention. Accordingly, it should be
understood that these statements are to be read in this light, and
not as admissions of prior art.
[0005] In the field of medicine, doctors often desire to monitor
certain physiological characteristics of their patients.
Accordingly, a wide variety of devices have been developed for
monitoring physiological characteristics of a patient. Such devices
provide doctors and other healthcare personnel with the information
they need to provide the best possible healthcare for their
patients. As a result, such monitoring devices have become an
indispensable part of modern medicine.
[0006] One technique for monitoring certain physiological
characteristics of a patient is commonly referred to as pulse
oximetry, and the devices built based upon pulse oximetry
techniques are commonly referred to as pulse oximeters. Pulse
oximetry may be used to measure various blood flow characteristics,
such as the blood-oxygen saturation of hemoglobin in arterial
blood, the volume of individual blood pulsations supplying the
tissue, and/or the rate of blood pulsations corresponding to each
heartbeat of a patient. In fact, the "pulse" in pulse oximetry
refers to the time varying amount of arterial blood in the tissue
during each cardiac cycle.
[0007] Pulse oximeters typically utilize a non-invasive sensor that
transmits light through a patient's tissue and that
photoelectrically senses the absorption and/or scattering of the
transmitted light in such tissue. One or more of the above
physiological characteristics may then be calculated based upon the
amount of light absorbed or scattered. More specifically, the light
passed through the tissue is typically selected to be of one or
more wavelengths that may be absorbed or scattered by the blood in
an amount correlative to the amount of the blood constituent
present in the blood. The amount of light absorbed and/or scattered
may then be used to estimate the amount of blood constituent in the
tissue using various algorithms. Changes in the amount of arterial
blood in the tissue during a blood pressure pulse may change the
amount and character of the light detected by the sensor's
photodetector.
[0008] The quality of the pulse oximetry measurement depends in
part on the concentration of arterial blood relative to other
tissue structures in the portion of the tissue illuminated by the
sensor and in part on the magnitude of the pulsatile changes in the
amount of blood in the tissue. Pulse oximetry techniques typically
utilize a tissue site that is well perfused with blood, such as a
patient's finger, toe, or earlobe, on which to place the sensor.
Although these sites are usually well perfused, blood flow to the
sensor site may be restricted due to the effects of ambient
temperature, systemically acting vasoconstricting drugs in the
patient's blood stream, or low blood pressure. The accuracy and
reliability of physiological measurements can be affected by the
amount of blood perfusion, as well as by the distribution of blood
flow within a tissue site. Furthermore, physiological differences
from patient to patient, or even from digit to digit, may cause
unintended variations in the measurements provided.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] Advantages of the invention may become apparent upon reading
the following detailed description and upon reference to the
drawings in which:
[0010] FIG. 1 illustrates an exemplary patient's fingers
illustrating bone and blood vessel placement;
[0011] FIGS. 2A, 2B, and 2C illustrate different views of an
exemplary patient's finger illustrating an exemplary cuticle region
and an exemplary distal region;
[0012] FIGS. 3A and 3D illustrate alternative embodiments of an
exemplary pulse oximetry sensor adapted for placement on a distal
region of a patient's digit;
[0013] FIG. 3B illustrates exemplary shunting characteristics of a
pulse oximetry sensor;
[0014] FIG. 3C illustrates a cross-section of the pulse oximetry
sensor of FIG. 3A with a shunt block;
[0015] FIGS. 4A, 4B and 4C illustrate alternative placements of the
emitter and detector of an exemplary pulse oximetry sensor in
accordance with the present invention.
[0016] FIG. 5A illustrates an exemplary bandage for securing the
pulse oximetry sensor of FIG. 3 to a patient's hand;
[0017] FIG. 5B illustrates a detailed view of the highlighted area
of FIG. 5A;
[0018] FIG. 6A illustrates a perspective view of an exemplary
clip-style pulse oximetry sensor on a patient's finger;
[0019] FIG. 6B illustrates a cross-sectional view of an exemplary
clip-style pulse oximetry sensor having an emitter and detector
located on a distal region of a patient's finger;
[0020] FIG. 6C illustrates a cross-sectional view of an exemplary
clip-style pulse oximetry sensor having an emitter and detector
located on a cuticle region of a patient's finger;
[0021] FIG. 7 illustrates a pulse oximetry system coupled to a
multi-parameter patient monitor;
[0022] FIG. 8A illustrates an exemplary photon distribution through
a patient's finger for a pulse oximetry sensor placed on a distal
region of a patient's finger;
[0023] FIG. 8B illustrates an exemplary photon distribution through
a patient's finger for a pulse oximetry sensor placed on a cuticle
region of a patient's finger;
[0024] FIG. 8C illustrates a cross-sectional view of an exemplary
clip-style pulse oximetry sensor having a light absorbing material
and having an emitter and detector located on a distal region of a
patient's finger with an exemplary photon distribution through the
patient's finger; and
[0025] FIG. 9 illustrates atop view of an exemplary patient's
finger illustrating an exemplary emitter aperture on a distal
region of the patient's finger.
DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS
[0026] One or more specific embodiments of the present invention
will be described below. In an effort to provide a concise
description of these embodiments, not all features of an actual
implementation are described in the specification. It should be
appreciated that in the development of any such actual
implementation, as in any engineering or design project, numerous
implementation-specific decisions must be made to achieve the
developers' specific goals, such as compliance with system-related
and business-related constraints, which may vary from one
implementation to another. Moreover, it should be appreciated that
such a development effort might be complex and time consuming, but
would nevertheless be a routine undertaking of design, fabrication,
and manufacture for those of ordinary skill having the benefit of
this disclosure.
[0027] As discussed previously, pulse oximetry sensors are
typically placed on a patient in a location that is normally
perfused with arterial blood to facilitate proper light absorption.
The most common sensor sites include a patient's fingertips, toes,
or earlobes. Pulse oximetry sensors used on these sensor sites are
typically "transmission type" sensors. Transmission type sensors
include an emitter and detector that are typically placed on
opposing sides of the sensor site. If the sensor site is a
fingertip, for example, the cuff, clip, or bandage associated with
the pulse oximetry sensor is positioned over the patient's
fingertip such that the emitter and detector lie on either side of
the patient's nail bed. In other words, the sensor is positioned so
that the emitter is located on the patient's fingernail and the
detector is located 180.degree. opposite the emitter on the
patient's finger pad. During operation, the emitter shines one or
more wavelengths of light through the patient's fingertip, and the
light received by the detector is processed to determine various
physiological characteristics of the patient. For determining the
oxygen saturation of the patient's arterial blood, two or more
wavelengths are used, most commonly red and near infrared
wavelengths.
[0028] Unfortunately, person-to-person and digit-to-digit
variability, as well as sensor placement variability, can cause
variability in the resulting pulse oximeter measurements. This
variability stems, in part, from the unique inhomogenity of the
vasculature within any specific sample of tissue and, in
particular, the moving and pulsing structures, e.g., the arteries,
within the tissue that non-linearly contribute to the optical
density of the probed tissue bed. Further, the presence of larger
subcutaneous vessels within the optically probed tissues may
influence the relationship between the modulation ratio of the
time-varying light transmission signals of the two or more
wavelengths and the underlying arterial oxygen saturation
measurement (SaO.sub.2). Also, simply shifting the placement
location of a sensor by as little as a few millimeters can result
in changes in the measured blood oxygen saturation (SpO.sub.2) of a
few percent.
[0029] To address these concerns, it would be desirable to find a
sensor site that is relatively void of larger semi-opaque vessels,
but that includes microvasulature, such as arterioles and
capillaries. Such a site would be well-perfused with arterial
blood, yet devoid of larger vessels and/or translucent structures
that might adversely affect the measurement capabilities of the
sensor. The hand structure 10 shown in FIG. 1 indicates that the
density of larger diameter arteries diminishes towards the distal
end of the fingertips. Hence, a pulse oximetry technique designed
to utilize the distal end of the fingertips, as opposed to a more
proximal region of the fingertips, as a sensor site would benefit
from tissue well-perfused with arterial blood, yet lacking larger
vessels and/or translucent structures that might adversely affect
the measurement capabilities of the sensor.
[0030] Looking also to FIGS. 2A, 2B, and 2C, a human finger, such
as the patient's index finger 12, includes three bones, called
phalanges. The bone that comprises the tip of the finger 12 is
commonly referred to as the third row phalange or the distal
phalange 14. On the exterior of the finger 12, the location of the
joint between the distal phalange 14 and the second row phalange 16
can be identified by the knuckle 18 on the top of the finger 12 and
by the transverse fold 20 of skin on the bottom of the finger
12.
[0031] The emitter and detector components of conventional pulse
oximetry sensors are located close to the cuticle region of the
fingernail, as indicated by the cuticle region 24 of the patient's
index finger 12. If the overall length L of the distal phalange 14
(covered with skin and other tissue) is defined to extend from the
tip 22 of the finger 12 to the transverse fold 20, then the cuticle
region 24 extends from a transverse line spaced from the tip by
about 35% of the length L to a transverse line spaced from the tip
22 by about 60% of the length L. In the cuticle region 24, several
arteries can be seen that are much larger in diameter than the
vasculature in the more distal region 26, which is defined herein
to extend from the tip 22 to a transverse line spaced from the tip
22 by about 20% to about 30% of the length L. Hence, this
conventional placement site in the cuticle region 24 is likely to
cause measurement variations from patient-to-patient.
[0032] Indeed, it should be noted that each of the digits of the
hand shown in the hand structure 10 have unique vessel locations.
Thus, the placement of a pulse oximetry sensor over a similar
cuticle region 24 of these digits may result in different signal
modulations unrelated to the underlying SaO.sub.2 level, since
these larger vessels are sufficiently opaque and, thus, may
non-linearly contribute to the optical density of the tissue.
Furthermore, small variations in the precise location of the sensor
optics in the cuticle region 24, or from digit-to-digit as
illustrated in this hand structure 10, may result in different
detected light levels due, in part, to the varying contribution of
the more opaque larger vasculature. In turn, this may impact the
detected red-to-infrared modulation ratio and, consequently, the
measured SpO.sub.2 value.
[0033] In sharp contrast, it should be noted that the distal region
26 of the index finger 12, i.e., the area extending from the tip 22
to a transverse line spaced from the tip 22 by between about 20% to
about 30% of the length L (approximately 5 mm to 7 mm from the tip
for an average adult finger), includes few, if any, larger diameter
arteries that may adversely affect pulse oximetry measurements.
Indeed, it appears that the light from a pulse oximeter sensor will
scatter through the tissue in the distal region 24 to probe the
smaller arterioles and capillaries more uniformly, since the light
fully penetrates these vessels. It is believed that this manner in
which the light probes the more uniform tissue results in a more
linear relationship between the modulating,i.e., cardiac-induced
time-varying, optical density of the tissue and the underlying
arterial blood oxygen saturation. As a further result, it is
believed that small variations in sensor placement in the distal
region 26, as well as different digit-to-digit placements, will
yield a more consistent relationship between the measured
red-to-infrared modulation ratio and the underlying SaO.sub.2 level
than is observed when sensors are placed more proximally in the
cuticle region 24.
[0034] To facilitate measurement in the distal region 26, a sensor
having an emitter and detector that may be located in the distal
region 26 of a patient's finger or toe is provided, and FIG. 3A
illustrates an exemplary pulse oximetry sensor 30 of this type. The
sensor 30 includes an emitter 32 and a detector 34 which may be of
any suitable type. For example, the emitter 32 may be one or more
light emitting diodes adapted to transmit one or more wavelengths
of light in the red to infrared range, and the detector 34 may be a
photodetector selected to receive light in the range emitted from
the emitter 32. The emitter 32 and the detector 34 may be disposed
on a substrate 36, which may be made of any suitable material, such
as plastic, foam, woven material, or paper. Alternatively, the
emitter 32 and the detector 34 may be located remotely and
optically coupled to the sensor using optical fibers. The substrate
36 may include an adhesive thereon to facilitate coupling of the
sensor 30 to the distal region 26 of a patient, although
alternative coupling arrangements are discussed below. Finally, the
sensor 30 is coupled to a cable 38 that is responsible for
transmitting electrical and/or optical signals to and from the
emitter 32 and detector 34 of the sensor 30. The cable 38 may be
permanently coupled to the sensor 30, or it may be removably
coupled to the sensor 30--the latter alternative being more useful
and cost efficient in situations where the sensor 30 is
disposable.
[0035] In one embodiment, the sensor 30 may be adapted to block
light that may shunt directly between the emitter 32 and the
detector 34, i.e., light that does not travel through the blood
perfused tissue of the finger 12. An example of two possible
shunting situations is illustrated in FIG. 3B. In one situation, a
"type 1" shunt may occur when light travels from the emitter 32 to
the detector 34 through the substrate 36, as illustrated by the
wavy arrow 35. In another situation, a "type 2" shunt may occur
when light travels from the emitter 32 to the detector 34 by
reflecting off of the finger 12, as illustrated by the wavy arrow
37. While the type 2 shunt is typically addressed by ensuring that
the sensor 30 is placed snuggly against the patient's finger 12,
the type 1 shunt may be addressed by placing a shunt barrier 39 in
or on the substrate 36 between the emitter 32 and the detector 34.
A "type 3" shunt, which is not illustrated, could also occur if
light passed through exsanguinated tissue.
[0036] In another embodiment, the sensor 30 may include regions
that differ in the manner in which they reflect and/or absorb light
from the emitter 32. As illustrated in FIG. 3D, it can be seen that
the region of the substrate 36 that extends from the emitter 32 to
the detector 34 may be a relatively light color, such as white, in
order to enhance the reflectivity of the substrate 36 on the
portion of the sensor 30 that is to be disposed on the distal
region 26 of a patient's finger 12. Portions 41 and 43 of the
substrate 36 that extend on either side of the emitter 32 and the
detector 34 may be a darker, i.e., more absorptive, color, such as
black. The darker portions 41 and 43 of the substrate 36 will tend
to absorb the light from the emitter 32 from portions of a
patient's finger 12 that may fall outside of the distal region 26
so that the light is not collected by the detector 34.
Consequently, it is more likely that light detected by the detector
34 has passed through tissue in the distal region 26 of the
patient's finger 12 as opposed to more proximal areas of the
patient's finger 12.
[0037] It should be appreciated that the emitter 32 and detector 34
of the sensor 30 may be placed in various positions in the distal
region 26 and may operate in various modes, e.g., transmission or
reflection. Examples of placement positions of the emitter 32 and
the detector 34 on a patient's finger 12 are illustrated in FIGS.
4A, 4B and 4C, although it should be appreciated that the emitter
32 and the detector 34 may be similarly placed on a patient's toe
as well. In FIG. 4A, it can be seen that the emitter 32 is located
on top of the finger 12 in the distal region 26, while the detector
34 is located underneath, i.e., on the finger pad, of the finger 12
in the distal region 26. The emitter 32 may lie slightly on the
fingernail 40, slightly under the fingernail 40, or on a fleshy
portion of the tip of the finger 12 that may protrude past the
fingernail 40. In this example, the emitter 32 and detector 34 can
be arranged in a transmission mode so that the light from the
emitter 32 shines vertically through the finger 12 to the detector
34. For a sensor 30 designed for use on a normally-sized adult, the
linear spacing between the center of the emitter 32 and the center
of the detector 34 on the substrate 36 would be in the range of
about 10 mm to about 20 mm to ensure that the emitter 32 and the
detector 34 are properly positioned in the distal region 26 of the
patient's finger when the sensor 30 is applied.
[0038] Alternate arrangements are illustrated in FIGS. 4B and 4C.
In FIG. 4B, it can be seen that the emitter 32 and the detector 34
are both located underneath the finger 12, i.e., on the finger pad,
in the distal region 26. Conversely, in FIG. 4C, it can be seen
that the emitter 32 and the detector 34 are both located on the top
of the finger 12 in the distal region 26. In the latter case, the
emitter 32 and the detector 34 may both be placed slightly on the
fingernail 40, slightly underneath the fingernail 40, or on the
fleshy region of the tip of the finger 12 that may protrude past
the fingernail 40. Because the emitter 32 and the detector 34 both
lie on the same side of the finger 12 in the alternatives
illustrated in FIGS. 4B and 4C, the emitter 32 and detector 34 may
be considered to operate in reflectance mode instead of
transmission mode. For a sensor 30 designed for use on a
normally-sized adult, the linear spacing between the center of the
emitter 32 and the center of the detector 34 on the substrate 36
would be in the range of about 5 mm to about 10 mm to ensure that
the emitter 32 and the detector 34 are properly positioned in the
distal region 26 of the patient's finger when the sensor 30 is
applied.
[0039] In each of the embodiments discussed herein, it should be
understood that the locations of the emitter and the detector may
be swapped. For example, in FIG. 4A, the detector 34 may be located
at the top of the finger 12 and the emitter 32 may be located
underneath the finger 12. In either arrangement, the components are
located in the distal region 26 and perform in substantially the
same manner.
[0040] The sensor 30 may be applied to a patient's finger or toe in
any suitable manner. One manner of application includes the use of
an adhesive bandage 42, as illustrated in FIGS. 5A and 5B. In this
example, the back of the substrate 36 is affixed to a portion of
the adhesive bandage 42 so that the emitter 32 and detector 34 may
be placed over the distal region 26 of the patient's finger 12. The
adhesive bandage 42 may be wrapped over the entire finger, or it
can be restricted to only a part of the finger. In this example,
the adhesive bandage 42 is applied primarily to the top of the
finger 12, where a portion of the bandage 42 extends along the
cable 38. The bandage 42 is first adhered to the left side of the
top of the patient's finger 12, extended to the right of the finger
12, around the distal region 26, and over to the right side of the
finger 12 in overlapping relationship with itself. Although the
illustrated example is believed to be particularly useful, any
other suitable configuration may also be used. For example, the
sensor 30 may be secured to the distal region 26 of a patient's
finger 12 by a non-adhesive wrap, a reusable wrap, or a clip.
[0041] One example of a clip-style sensor 30A is illustrated in
FIGS. 6A, 6B, and 6C. The sensor 30A is illustrated as having two
halves or portions. In this embodiment, the sendor 30A is
configured to operate in transmission mode, so the emitter resides
in one half and the detector resides in the other half. In an
alternate embodiment (not shown), the sensor 30A may be configured
to operate in reflectance mode, in which case the emitter and the
detector would reside in the same half or portion. In either case,
the sensor 30A is spring loaded so that the sensor 30A is biased in
a closed position about a patient's finger 12, as illustrated. As
best seen in FIG. 6B, the sensor 30A includes a stop 49 upon which
a patient's finger 12 is intended to rest when the patient's finger
12 is properly inserted into the clip-style sensor 30A. When the
patient's finger 12 is properly inserted against the stop 49, the
emitter 32 and the detector 34 lie in the distal region 26 of the
patient's finger 12. In contrast to the sensor 30A illustrated in
FIG. 6B, FIG. 6C illustrates a clip-style sensor 51 having a stop
53. As can be seen in FIG. 6C, when the patient's finger 12 is
inserted to abut against the stop 53, the emitter 64 and the
detector 66 are located in the cuticle region 24 of the patient's
finger 12. Hence, it can be readily appreciated that the distance
that the emitter and detector are spaced apart from the stop
dictates whether the sensor is suitable for facilitating
measurement in the distal region 26 or the cuticle region 24.
[0042] Regardless of type, the sensor 30 is typically adapted to be
coupled directly to a pulse oximetry monitor 50, as illustrated in
FIG. 7. However, it should be appreciated, that the cable 38 of the
sensor 30 may be coupled to a transmission device (not shown) to
facilitate wireless transmission between the sensor 30 and the
monitor 50. The monitor 50 may be any suitable pulse oximeter, such
as those available from Nellcor Puritan Bennett Inc. Furthermore,
to upgrade conventional pulse oximetry provided by the monitor 50
to provide additional functions, the monitor 50 may be coupled to a
multi-parameter patient monitor or other pulse oximetry monitor 52
via a cable 54 connected to a sensor input port or via a cable 55
connected to a digital communication port.
[0043] Once the sensor 30 is suitably applied to the distal region
26 of the patient's finger 12 and coupled to a suitable pulse
oximetry monitor, the emitter 32 will transmit the selected
wavelength(s) of light into the distal region 26 of the patient's
finger 12 and the detector 34 will detect light from the distal
region 26 of the patient's finger 12. As illustrated in FIG. 8A,
the photon distribution 60 illustrates the amount of light emitted
from the emitter 32 that passes through various portions of the
patient's finger 12 and that is detected by the detector 34. In
other words, the photon distribution 60 is a graphical
representation of where the photons from the emitter 32 travel
through the tissue for ultimate receipt by the detector 34. With
the emitter 32 and detector 34 located in the distal region 26 of
the patient's finger 12, it can be seen that the majority of the
photons received by the detector 34 pass through the distal region
26, with a minority of the photons received by the detector 34
passing through the cuticle region 24. Indeed, it is estimated that
at least approximately 50% to 80%, and possibly 90% or more, of the
light received by the detector 34 has passed through the distal
region 26 when the sensor 30 is located in the distal region 26 of
the patient's finger 12.
[0044] In contrast, FIG. 8B illustrates a photon distribution 62
created by a conventional sensor located in the cuticle region 24
of a patient's finger. The photon distribution 62 illustrates the
amount of light emitted from an emitter 64 that passes through
various portions of the patient's finger 12 and that is detected by
a detector 66. Similar to the photon distribution 60, the photon
distribution 62 is a graphical representation of where the photons
from the emitter 64 travel through the tissue for ultimate receipt
by the detector 66. With the emitter 64 and detector 66 located in
the cuticle region 24 of the patient's finger 12, it can be seen
that the majority of the photons received by the detector 66 pass
through the cuticle region 24, with a minority of the photons
received by the detector 66 passing through the distal region 26.
Indeed, it is estimated that approximately 65% to 85% of the light
received by the detector 66 has passed through the cuticle region
24 when the sensor is located in the cuticle region 24 of the
patient's finger 12, whereas only approximately 15% to 35% of the
light received by the detector 66 has passed through the distal
region 26.
[0045] As demonstrated by the exemplary photon distributions 60 and
62 illustrated in FIGS. 8A and 8B, the placement of an emitter and
detector in the distal region 26 of a patient's finger 12 results
in much more of the detected light having passed through the
well-perfused and relatively unoccluded tissue of the distal region
26, as opposed to the relatively occluded tissue of the cuticle
region 24, when compared with the placement of an emitter and
detector in the conventional cuticle region 24 of a patent's
finger. As a result, the collected light presumably correlates
better with the characteristics of the blood that the pulse
oximeter 50 is attempting to measure, since the collected light is
not as adversely affected by strongly light-absorbing or scattering
structures, such as bones and larger blood vessels.
[0046] Although the present drawings illustrate the emitter 32 and
the detector 34 as being wholly located in the distal region 26, it
should be noted that similar results will likely follow so long as
the center points of the emitter 32 and detector 34 are located in
the distal region 26 even though a portion of the emitter 32 and/or
detector 34 might lie in the cuticle region 24. Indeed, in a
possible embodiment in which the emitter 32 and/or the detector 34
have relatively large diameters, in the range of about 5 mm to
about 10 mm for example, a portion of the emitter 32 and/or
detector 34 might lie in the cuticle region 24, even though the
emitter 32 and the detector 34 are centered over the distal region
26. Nevertheless, it is believed that such a sensor placement would
result in benefits similar to those discussed above in embodiments
in which the emitter 32 and the detector 34 are wholly located in
the distal region 26 without extending into the cuticle region
24.
[0047] To improve the concentration of light in the distal region
26 as opposed to the cuticle region 24, the sensor 30/30A may be
provided with portions of light absorbing material in the areas of
the sensor 30/30A proximate to the cuticle region 24 and portions
of relatively reflective material in portions of the sensor 30/30A
proximate to the distal region 26. As discussed previously, FIG. 3D
illustrates a sensor 30 having portions 41 and 43 of relatively
light absorbing material to facilitate such an improvement in
photon distribution in the distal region 26. Further, FIG. 8C
illustrates a clip-style sensor 30A that includes portions 67 and
69 of relatively light absorbing material that extends along the
portions of the sensor 30A that are proximate the cuticle region
24. As illustrated by the exemplary photon distribution 61, the
portions 67 and 69 of light absorbing material greatly reduce the
amount of light from the emitter 32 that passes through the cuticle
region 24 to be received by the detector 34. Hence, the collected
light presumably correlates better with the characteristics of the
blood that the pulse oximeter 50 is attempting to measure, since
the collected light is not as adversely effected by structures in
the cuticle region 24 of the patient's finger 12.
[0048] Alternatively, or in addition to, the above techniques, the
emitter, or the aperture through which the emitter transmits light,
may be shaped to enhance the concentration of photons delivered to
the distal region 26. Referring to FIG. 9, an example of such an
emitter/aperture 32A is illustrated. As can be seen, the
emitter/aperture 32A is shaped so that it extends laterally across
the distal region 26 to deliver photons having a distribution
pattern that is more focused and better distributed within the
distal region 26 as compared with a round emitter/aperture.
[0049] While the invention may be susceptible to various
modifications and alternative forms, specific embodiments have been
shown by way of example in the drawings and have been described in
detail herein. However, it should be understood that the invention
is not intended to be limited to the particular forms disclosed.
Indeed, the present techniques may not only be applied to
measurements of blood oxygen saturation, but these techniques may
also be utilized for the measurement and/or analysis of other blood
constituents using principles of pulse oximetry. For example, using
the same, different, or additional wavelengths, the present
techniques may be utilized for the measurement and/or analysis of
carboxyhemoglobin, met-hemoglobin, total hemoglobin, intravascular
dyes, and/or water content. Rather, the invention is to cover all
modifications, equivalents, and alternatives falling within the
spirit and scope of the invention as defined by the following
appended claims.
* * * * *